Electric motors and generators are machines that have been around for a long time. Currently high efficiency large electric machines, i.e., those with a rating of greater than 10 horsepower (HP) and often greater than 100 hp, use wound field synchronous devices with expensive control mechanisms and small machines, i.e., those rated at 10 HP or less, use rare earth rotor magnet devices or induction rotor field devices. Rare earth rotor magnet devices are expected to increase in price in coming years and induction rotor field devices are inefficient energy-wise.
Projected increases in the cost of energy both economically and environmentally, have led to a need for motors and generators that are both low cost and energy efficient.